Digestive System and Nutrition

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Chapter 8

• Digestive System and Nutrition

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Points to Ponder

• What are the digestive system structures and
  their functions?
• Where does carbohydrate, protein and fat
  digestion and absorption occur?
• What are proteins, lipids, carbohydrates,
  minerals and vitamins needed for?
• What is an essential vs. a nonessential nutrient?
• What are the 3 accessory organs of digestion?
• What is obesity and why is it a problem?
• What is LDL and HDL?
• What are the components of a healthy diet?
• Name and explain 4 eating disorders.

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Main steps in the digestive process?
8.1 Overview of digestion

• 1. Ingestion intake of food via the mouth
• 2. Digestion mechanically or chemically
  breaking down food into their subunits
• All parts of the tract, except the large
  intestines, contain digestive enzymes
• Enzymes hydrolyze foods to molecular nutrients
• Chyme ? thick semifluid mass of partly digested
  food
• 3. Movement food must be moved along the GI
  tract in order to fulfill all functions
• 4. Absorption movement of nutrients across the
  GI tract wall to be delivered to cell via the
  blood
• 5. Elimination removal of indigestible
  molecules

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The 4 major layers of the GI tract wall
8.1 Overview of digestion

• Lumen central space that contains water
• Mucosa innermost layer that produces mucus
• protect the lining
• produce digestive enzymes
• Submucosa 2nd layer of loose connective tissue
• contains blood vessels, lymphatic vessels and
  nerves
• Lymph nodules ? protect against disease
• Muscularis 3rd layer made of 2 layers of smooth
  muscle (inner circular outer longitudinal)
• move food along the GI tract
• Under nerve control
• Serosa outer lining that is part of the
  peritoneum
• - Secretes serous fluid

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Layers of the GI tract
8.1 Overview of digestion
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8.1 Overview of digestion
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The Pathway that food follows
8.1 Overview of digestion

• mouth
• pharynx
• esophagus
• stomach
• small intestine
• large intestine
• rectum
• anus

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The first part of the digestive tract includes
the
8.2 First part of the digestive tract

• Mouth
• Pharynx
• Esophagus

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The mouth
8.2 First part of the digestive tract

• Chemical Digestion
• 3 pairs of salivary glands secrete salivary
  amylase
• begins carbohydrate digestion
• Mechanical Digestion
• Teeth begin the mechanical breakdown of food
• Roof two parts
• Hard Palate - bone
• Soft Palate muscle, ends at the uvula
• Tonsils lymphatic tissue
• back of the mouth and in the nasopharynx
• important in fighting disease
• Tongue
• is covered by mucous membrane with taste buds
  (sensory receptors)
• Activated taste buds cause ? nerve impulse to the
  brain
• Skeletal muscle that assists in mechanical
  breakdown and movement of food
• The tongue forms a bolus (mass of chewed food)
  and moves it toward the pharynx

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Anatomy of the mouth
8.2 First part of the digestive tract
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Teeth
8.2 First part of the digestive tract

• 32 in adults used for mechanical breakdown of
  food (20 deciduous teeth in babies)
• Two Parts
• 1. Crown
• Enamel Hard covering of calcium compounds
• Dentin thick layer of bonelike material
• Inner pulp contains nerves and blood vessels
• 2. Root
• Dentin and inner pulp
• Dental cavities tooth decay
• bacteria metabolize sugars and produce acids
• limiting sugar intake and brushing teeth reduces
  cavities

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Anatomy of a tooth
8.2 First part of the digestive tract
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The pharynx and esophagus
8.2 First part of the digestive tract

• Pharynx is a cavity between the mouth and
  esophagus that serves as a passageway for food
  (and air)
• Esophagus is a long, muscular tube that carries
  food to the stomach

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How do we swallow food?
8.2 First part of the digestive tract

• Voluntary phase Swallowing
• The beginning of food being swallowed from the
  mouth into the pharynx
• Involuntary phase
• Once the food is in the pharynx swallowing
  becomes a reflex
• The epiglottis covers the voice box to make sure
  food is routed into the esophagus
• Food moves down the esophagus through peristalsis
  (rhythmic contraction)

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Heartburn
8.2 First part of the digestive tract

• Sphincter Muscle that encircles tubes and act
  as valves
• Open relaxation
• Closed contraction
• Lower gastroesophageal sphincter
• Contraction prevents the acidic contents of
  stomach from backing up into esophagus
• Heartburn occurs when acids from the stomach pass
  into the esophagus (acid reflux)
• Burning sensation in the esophagus
• Chronic heartburn gastroesophageal reflux
  disease (GERD)
• Tips for decreasing heartburn
• Avoid high fat meals
• Dont overeat
• Eat several small meals rather than the standard
  3 larger meals each day
• Exercise lightly

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How do we swallow food?
8.2 First part of the digestive tract
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The stomach
8.3 The stomach and small intestine

• Functions
• to store food
• start digestion of proteins
• control movement of chyme into the small
  intestine
• NOT involved in absorption
• J-shaped organ with a thick wall
• Wall 4 layers
• 1-3. Muscular layer 3 layers of smooth muscle
• 4. Mucosa layer

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The Stomach

• Stomach Wall 4 layers
• 3 layers of smooth muscle in the muscularis layer
  of the stomach wall
• Circular, Longitudinal, and Oblique
• Helps mechanical digest and allowing stomach to
  stretch
• Mucosa layer
• deep folds called rugae
• Has gastric pits that lead into gastric glands
  that secretes gastric juice
• Gastric juice contains pepsin, HCL and mucus
• enzyme that breaks down proteins
• HCl gives the stomach a pH of 2
• activates pepsin and helps kill bacteria found in
  food
• A bacterium, Helicobacter pylori, lives in the
  mucus and can cause gastric ulcers
• The stomach empties chyme into the small
  intestine after 2-6 hrs.
• Peristaltic waves move it toward the pyloric
  sphincter

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Anatomy of the stomach
8.3 The stomach and small intestine
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The small intestine
8.3 The stomach and small intestine

• Averages 6m (18 ft) in length
• Enzymes secreted by the pancreas into the
  duodenum (small intestine)
• digest carbohydrates, proteins and fats
• Bile
• secreted by the gallbladder into the duodenum
• emulsify fats resulting in fat droplets
• Pancreatic Juices
• Lipase hydrolyze fat droplets ? glycerol and
  fatty acids
• Pancreatic amylase digest carbohydrates ? glucose
• Pancreatic trypsin digests proteins ? amino acids
• Pancreatic juices
• neutralizes chyme and causes the intestines to
  have a slightly basic pH

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The Small Intestines

• Absorbs sugars, amino acids, fatty acids, and
  glycerol
• Mucosa contains fingerlike projections villi
• Villus outer layer of columnar epithelial cells
• Each cell thousands of microvilli, make brush
  boarder
• Microvilli bear intestinal enzymes
• Microvilli increase surface area for increased
  absorption
• Villus
• Contains capillaries and small lymphatic
  capillary (lacteal)
• Amino acids and sugars enter the capillaries
• Fatty acids and glycerol enter the epithelial
  cells of villi
• Digested fats are joined and packaged as
  lipoprotein droplets
• Droplets chylomicrons
• enter lacteals (small lymph vessels)

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Anatomy of the small intestine
8.3 The stomach and small intestine
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How are nutrients digested and transported out of
the small intestine?
8.3 The stomach and small intestine
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Major Digestive Enzymes
8.3 The stomach and small intestine
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The three accessory organs
8.4 Three accessory organs and regulation of
secretions

• Pancreas
• Liver
• Gallbladder

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The Pancreas
8.4 Three accessory organs and regulation of
secretions

• Fished-shaped spongy organ behind the stomach
• Functions of the pancreas
• 1. Secretes enzymes into the small intestine
• Trypsin digests proteins
• Lipase digests fats
• Pancreatic amylase digests carbohydrates
• 2. Secretes bicarbonate into the small intestine
  to neutralize stomach acids
• 3. Secretes insulin into the blood to keep blood
  sugar levels under control

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The liver and gallbladder
8.4 Three accessory organs and regulation of
secretions

• Large metabolic organ
• lies under the diaphragm and is made of 100,000
  lobules
• Filters blood from the GI tract
• acting to remove poisons and detoxify the blood
• Removes iron, vitamins A, D, E, K and B12 from
  blood and stores them
• Stores glucose as glycogen
• Breaks glycogen down to help retain blood glucose
  levels
• Makes plasma proteins and helps regulate
  cholesterol levels by making bile salts
• Makes bile that is then stored in the gallbladder
  
• Secreted into the small intestine to emulsify
  fats
• Increase surface area of fat droplets
• Breaks down hemoglobin producing bilirubin
• Gallstones hardening or liquid stored in the
  gallbladder

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Liver disorders
8.4 Three accessory organs and regulation of
secretions

• Hepatitis
• Inflammation of the liver
• Caused by Hepatitis A, B and C
• A (from water) and B (from sexual contact) have
  vaccinations
• C (from contact with infected blood) has no
  vaccination
• This can lead to liver damage, cancer and/or
  death
• Cirrhosis
• The liver becomes fatty and eventually this
  tissue is replaced by fibrous scar tissue
• Seen in alcoholics and obese people
• This can lead to liver failure in which the liver
  cannot regenerate as fast as it is being damaged

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Hormones control digestive gland secretions
8.4 Three accessory organs and regulation of
secretions
Stomach Gastrin produced when diet is rich in
protein - enters circulation and
increases activity of gastric
glands Duodenum Secretin HCl in chyme
stimulates relese of secretin CCK released
while partially digested protein and fats are
present - stimulates release of bile
Secretin and CCK Inc. release of pancreatic
juices - digest food and buffer chyme
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The large intestine
8.5 The large intestine and defecation

• Includes the cecum, colon, rectum and anal canal
• Larger in diameter but shorter than the small
  intestine
• The cecum has a projection known as the appendix
  that may play a role in fighting infections
• Functions to
• Absorb water to prevent dehydration
• Absorbs vitamins (B complex and K) produced by
  intestinal flora (bacteria)
• Forms and rids the body of feces through the anus

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The Large Intestines

• Defecation
• 1. Peristalsis forces feces into the rectum
• 2. Stretching of the rectal wall initiates nerve
  impulses to the spinal cord
• 3. Rectal muscles contract and anal sphincters
  relax
• 4. Feces exit the body

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Disorders of the colon and rectum

• Diarrhea
• increased peristalsis
• water is not reabsorbed due to either an
  infection or nervous stimulation
• Constipation
• condition when feces are dry and hard
• may be controlled with water and fiber
• Hemorrhoids
• enlarged and inflamed blood vessels of the anus
• due to chronic constipation, pregnancy, aging and
  anal intercourse
• Diverticulosis
• occurrence of pouches of mucosa from weak spots
  in the muscularis layer that can become infected
  often in the colon
• Irritable bowel syndrome (IBS)
• muscularis layer contracts with power but without
  its normal coordination
• characterized by chronic diarrhea and abdominal
  pain
• Inflammatory bowel disease/colitis (IBD)
• group of inflammatory disorders such as
  ulcerative colitis or Crohns disease
• Polyps and cancer
• small growths found in the epithelial lining that
  can be benign or cancerous

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What is obesity and BMI?
8.6 Nutrition and weight control

• When an individual is grossly overweight and has
  a body mass index (BMI) 30
• BMI is a general guide to estimate how much of a
  persons weight is due to adipose tissue
• It does not take into account gender, fitness or
  bone structure

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What is your BMI?
8.6 Nutrition and weight control
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Why should we be concerned with obesity?
8.6 Nutrition and weight control

• Has doubled in the US in the last 20 years
• In the US 1/3 of adults are obese and it is now
  prevalent in children and adolescents
• Obesity tends to increase with an increase in
  income
• Is associated with in increased risk of premature
  death, Type 2 diabetes, hypertension, CVD,
  stroke, gallbladder disease, respiratory
  disfunction, osteoarthritis and certain cancers

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Searching for the magic weight-loss bullet
8.6 Nutrition and weight control

• Trendy diet programs
• Pritikin diet high carbohydrate and fiber diet
  through whole grains and vegetables
• Atkins low-carbohydrate and high protein and
  fat diet
• Zone and South beach diet low carbohydrate with
  a high protein and healthy fat diet
• Prescription drugs
• Surgical procedures
• Gastroplasty
• stapling or partitioning of a small portion of
  the stomach
• Gastric bypass
• attaching the lower part of the small intestine
  to the stomach so most of the food bypasses the
  stomach and small intestine
• Gastric banding
• constriction band is used to reduce stomach size
• Liposuction
• removal of fat cells best used for overweight
  people that are not obese or morbidly obese

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To understand weight and nutrition we first have
to understand nutrients
8.6 Nutrition and weight control

• Nutrients is a component of food that is needed
  to perform a physiological body function
• Nutrients include
• Carbohydrates
• Proteins
• Lipids
• Minerals
• Vitamins

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Carbohydrates
8.6 Nutrition and weight control

• Sugars or polysaccharides
• digested into simple sugars that are an important
  energy source
• Refined grains
• should be minimized in the diet because fiber and
  vitamins are removed (i.e. white bread, cake and
  cookies)
• Complex carbohydrates
• are recommended as a good source of vitamins and
  minerals (i.e. beans, whole-grain products, nuts
  and fruits)

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Can carbohydrates be harmful?
8.6 Nutrition and weight control

• Refined sugars and fructose sweeteners may
  contribute to obesity
• These foods may cause the pancreas to secrete
  large amounts of insulin
• lead to insulin resistance seen in type 2
  diabetes and increased fat metabolism
• An increase in fat deposition may increase risk
  of
• coronary heart disease, liver diseases and
  certain cancers

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8.6 Nutrition and weight control
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Proteins
8.6 Nutrition and weight control

• Proteins are digested into 20 different amino
  acids
• used to produce cellular proteins
• Essential amino acids are the 8 amino acids
• must be attained through diet
• Complete proteins that have all essential amino
  acids
• usually derived from animals such as meat and
  dairy
• Non-animal sources of complete proteins are tofu,
  soymilk and other processed food from soybeans
• Incomplete proteins are ones that lack at least
  one essential amino acid (i.e. legumes, nuts,
  grains etc)
• need to be combined with another incomplete
  protein to allow all amino acids to be used in
  the body
• Amino acids cannot be stored in the body
• small amounts (2 meat servings) need to be
  ingested on a daily basis

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Can proteins be harmful?
8.6 Nutrition and weight control

• An overabundance of protein
• can result in dehydration during exercise and
  sweating
• An overabundance of proteins
• can lead to calcium loss in urine which can lead
  to kidney stones
• Eating red meat as a source of protein is high in
  saturated fats that can lead to CVD

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Lipids
8.6 Nutrition and weight control

• Includes fats, oils and cholesterol
• Saturated fats (usually of animal origin)
• usually solid at room temperature while
  unsaturated fats are usually liquid at room
  temperature
• Essential fatty acids are ones that must be
  ingested
• linoleic acid and linolenic acid
• found in polyunsaturated oils such as corn and
  safflower
• Olive and canola oil contain monounsaturated fats
• Omega-3 fatty acids are thought to ward of heart
  disease
• found in some fish (salmon, sardines and trout)
  as well as some plants (flaxseed oil)

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Choosing the most healthy fat and oil
8.6 Nutrition and weight control
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Can lipids be harmful?
8.6 Nutrition and weight control

• CVD is often a result of arteries blocked by
  plaque
• Plaque made of cholesterol and saturated fats
• Low density lipoproteins (LDL) is the bad
  cholesterol
• it carries cholesterol from the liver to the
  cells
• LDL
• increased by saturated fats and decreased by
  unsaturated fats
• High density lipoproteins (HDL) is the good
  cholesterol
• it carries cholesterol to the liver where it is
  converted to bile salts
• Trans-fatty acids
• made by hydrogenation of unsaturated fatty acids
  for commercial products and may reduce the
  ability of cells to clear cholesterol from the
  bloodstream

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8.6 Nutrition and weight control
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Minerals
8.6 Nutrition and weight control

• The body contains gt 5g of each major mineral and
  lt 5g of each trace mineral
• Major minerals make up components of cells, body
  fluids and tissues (i.e. calcium)
• Minor minerals are components of larger molecules
  (i.e. iron in hemoglobin)
• A varied and complete diet usually provides
  necessary minerals

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Calcium
8.6 Nutrition and weight control

• Needed to make bone, nerve impulse conduction and
  muscle contraction
• 1,000mg/day are recommended to keep bones healthy
  early in life and 1,300mg/day after menopausal
  age
• Vitamin D is needed with calcium to prevent bone
  loss (osteoporosis)

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Sodium
8.6 Nutrition and weight control

• Needed for regulating water balance
• 500mg/day is the recommended amount (on average
  each American takes in 4,000 - 4,700mg/day)
• Sodium can increase hypertension in people who
  already have it

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8.6 Nutrition and weight control
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Vitamins
8.6 Nutrition and weight control

• Organic compounds (not including proteins, fats
  or carbohydrates)
• used for metabolism but are not produced in high
  enough quantity by the body
• Vitamins are often enzyme helpers (coenzymes)
• There are a total of 13 vitamins in two groups
• fat-soluble and water soluble

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Fat-soluble vitamins
8.6 Nutrition and weight control
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Water-soluble vitamins
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Antioxidants
8.6 Nutrition and weight control

• Are chemicals that decrease the rate of oxidation
  or transfer of electrons
• Vitamin C, E and A are considered antioxidants
  because they are thought to defend the body
  against free radicals that can transfer electrons
  and damage cells and DNA
• The vitamins are common in fruits and vegetables

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A guide to daily food recommendations
8.6 Nutrition and weight control
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Eating disorders
8.6 Nutrition and weight control

• Anorexia nervosa
• psychological disorder due to fear of getting fat
  
• usually results in self-induced starvation, high
  physical activity and may include purging
• Bulimia nervosa
• disorder in which people eat large amounts of
  high-calorie food (binge-eating) followed by
  purging to avoid weight gain often more than once
  a day
• Binge-eating disorder
• obese people are afflicted in which overeating is
  not followed by purging that can lead to
  depression, anger, anxiety and more binges
• Muscle dysmorphia
• by people that think their bodies are
  underdeveloped and are often preoccupied with
  body-building activities and diet

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Eating disorders are associated with body image
8.6 Nutrition and weight control